Technical Field
[0001] The present invention relates to a fuel injection system for internal combustion
engines and more particularly to an electronically controlled injection system. Since
the system operates at a high fuel pressure, it is particularly suited for the direct
injection of fuel into the combustion chamber of each cylinder of the internal combustion
engine. This injection system can be used advantageously in diesel engines.
Background and Summary of the Invention
[0002] Different designs of fuel injection systems are disclosed in the following publications:
[0003] German published patent application 32 27 742 (corresponding to U.S. patent specification
4,566,416); U.K. published patent application 2 165 895 (corresponding to U.S. patent
specification 4,633,837); German published patent application 31 26 393 (corresponding
to U.K. patent application 80 21 836); German published patent application 29 07 279;
French published patent application 2 546 237 (corresponding to U.S. patent specifica
tion 4,535,742) and French patent specification 1,176,110 (corresponding to U.K. patent
specification 818 197).
[0004] In German published patent application 32 27 742 and U.S. patent specification 4,566,416
an injection system is disclosed employing injectors provided with an accumulator
volume or chamber with a volume substantially larger than the maximum volume of fuel
injected during each injection event. This accumulator chamber is located in the injector
body upstream of the seat of the injector needle valve. The injection orifices are
located downstream of this seat. These orifices communicate with the combustion chamber
of the related internal combustion engine. The fuel stored in the accumulator chamber
under high pressure is partly discharged through the injection orifices during each
injection event with a simultaneous pressure drop in the accumulator chamber. The
injector accumulator communicates with the high pressure fuel supply line of the injection
system by means of a restricted passage or orifice. The orifice, due to its small
cross-sectional flow area, prevents the formation of noticeable pressure waves in
the fuel supply lines during each injection event. Such pressure waves would highly
affect the uniform fuel distribution in a multicylinder engine and the stability of
the injection events of a single injector from cycle to cycle.
[0005] To obtain good engine performance with respect to engine power, efficiency and emissions,
a very uniform fuel distribution from cylinder to cylinder must be achieved in a multicylinder
engine at each engine operating point. The same holds true for each injector from
cycle to cycle. In addition to said orifice between each injector accumula tor and
the fuel supply line, a plenum fuel chamber communicating with the fuel supply lines
of all injectors of the injection system is provided in order to achieve the desired
uniform fuel distribution. Due to its relatively large volume, the plenum chamber
evens out the pressure pulsations created by the high pressure fuel supply pump and
thus creates a constant pressure level for all injectors. At different points in the
engine operating range, different fuel injection pressures are required. As an example,
it is advantageous to use a low injection pressure at low engine load and at idling
and a high injection pressure at high engine load and high speed.
[0006] In a passenger car engine, transient speed and load conditions are the most often
encountered situation, and the injection system pressure must be able to rapidly respond
to the variing driver demands. It must be possible to rapidly increase and drop the
fuel pressure in the plenum chamber. Due to its large volume, this is a difficult
task to accomplish.
[0007] In the injection system disclose d in UK published patent application 2 165
895 and the corresponding U.S. patent specification 4,633,837 the fuel metered by
a high pressure pump is delivered to a fuel manifold. Fuel lines lead from this manifold
to the injectors. In each line section connecting one injector to the fuel manifold
there is placed an electrically operated on/off valve. To allow for the momentary
injection of fuel by an injector, the on/off valve must be opened. The injector needle
valve will subsequently be opened against the closing bias force of a spring by the
fuel pressure propagating from the on/off valve to the needle valve seat. To terminate
each one such momentary injection event, the on/off valve must be closed to allow
the fuel pressure at the injector to drop below the bias force of the needle valve
spring which consequently closes the injector needle valve. In the period between
two injection events of one injector the pressure in the line section between the
on/off valve to the injection valve seat is lower than the injector needle valve opening
pressure and thus substantially lower than the injection pressure during the injection
event. The acutal injection pressure at the end of the injection event is low, according
to the closing force of the injector needle valve spring, which results in poor fuel
atomisation and increased polluant emissions of the related internal combustion engine.
[0008] In the injection system of the German published patent application 31 26 393 fuel
is delivered under high pressure to a fuel chamber similar to the plenum chamber disclosed
in the aforementioned German published patent application 32 27 742. From this chamber
fuel is fed by fuel lines of a small inner diameter to the injectors of the injection
system. The pressure drop at each injector during each injection event is used to
control the fuel delivered by each injector into the combustion chamber of the related
internal combustion engine. This last system appears to have the same basic disadvantage
as the system disclosed in German published patent application 32 27 742 discussed
earlier, namely poor response of the system pressure during transient engine operation.
[0009] It is now an object of the present invention to provide a new and improved fuel injection
system, which allows to eliminate the above-mentioned plenum chamber required in prior
art injection systems while maintaining a uniform fuel distribution at each engine
operating point.
[0010] This object is accomplished by a fuel injection system as defined in claim 1.
[0011] Each injector of the injection system of the present invention is electromagnetically
operated. The injector needle valve is opended and closed by the pressures acting
on both sided of a needle valve piston. An electromagnetically operated valve controls
the fuel pressure at the top end of the needle valve piston. In this way, it is possible
to open and to close the injector needle valve at a fuel pressure level, in the region
immediately upstream of the seat of the injector needle valve, almost as high as a
the highest pressure during each intermittent injection event, with consequently good
fuel atomisation and reduced polluant emissions of the related internal combustion
engine.
[0012] Furthermore, the new and improved design of the injector needle valve piston of each
injector allows to eliminate the injector accumulator chamber as well as the orifice
between each injector accumulator and the fuel supply line of the prior art fuel injection
systems. Because of the novel design of the injector needle valve piston, it is no
longer important that the pressure level in the fuel supply line to each injector
remains constant. Pressure pulsations are thus allowed, as long as they are the same
for all injectors.
[0013] Those and further advantages of the invention will be readily apparent from the following
detailed description of preferred embodiments of the present invention shown in the
accompanying drawing.
Brief Description of the Drawings
[0014]
Fig. 1 is a schematical view of an electronically controlled injection system in accordance
with the present invention;
Fig. 2 is an enlarged fragmentary axial sectional view of an embodiment of an injector
used in the injection system in accordance with the present invention, showing the
design of the injector needle piston;
Fig. 3 is a schematical view of an alternate embodiment of the electronically controlled
injection system shown in Fig. 1; and
Fig. 4 is a schemetical view of a second alternate embodiment of the electronically
controlled injection system shown in Fig. 1.
Detailed Description of the Preferred Embodiments
[0015] Turning to the Figures wherein like numerals are employed for identifying like parts,
the proposed electronically controlled injection system is employed in a four cylinder
engine, designated by the numeral 2. On the upper part of the engine 2 there are placed
four electronically controlled injectors 4 to inject pressurized fuel into the combustion
chamber (not shown) of the engine 2. The fuel comes from a fuel tank 6 and reaches
through a low pressure pipe 6a a fuel filter 8 and through another low pressure pipe
9 a high pressure pump 10. The drive shaft 5 of pump 10, which can be a one- or multicylinder
pump, depending on the specific application, is driven by a shaft 3 of the engine
2 with a constant drive ratio, for example by means of a gear or a tooth-belt 11.
As an important matter, the motion of the plunger or plungers of pump 10 shall be
harmonic and each pumping event shall take place over a large angle of rotation of
the pump drive shaft 5 and thus also of the engine's crankshaft 7. Preferably, the
maximum fuel delivery of the pump 10 per revolution of the engine crankshaft 7 shall
be substantially equal to the maximum fuel quantity delivered to the engine and spilled
back to the tank by the totality of the injectors 4 of the injection system in one
revolution of the engine crankshaft 7.
[0016] Furthermore the number of pumping strokes taking place shall be the same or an entire
multiple of the number of injection events. In the case of the embodiment of Fig.
1, and supposed the engine 2 is a four cycle engine, two combustion events and thus
two injection events take place during each revolution of the engine's crankshaft
7. In this case one could use a two-plunger pump 10 driven by the engine 2 with a
drive ratio of 1:1 in order to obtain the same number of pumping strokes and injection
events. Each pumping event would then take place during an 180 degrees rotation of
crankshaft 7. Since the pumping event takes place over a wide angle of rotation of
the crank shaft 7 and the injection event is of a relatively short duration, there
is no relationship between the momentary pumping rate of any of the pumping plungers
of pump 10 and the injection rate of any of the injectors 4. Nevertheless it is suitable
that the injection event of each of the injectors 4 of the injection system takes
place during the pumping stroke of any one of the pumping plungers of the pump 10.
[0017] For the same four cylinder engine 2 as shown in Fig. 1, one could also use a single-plunger
pump 10 driven by the engine 2 with a drive ratio between pump shaft 5 and crankshaft
7 of 2:1. Also a single-plunger pump 10 driven with a 1:1 drive ratio but with a construction
providing two strokes of the plunger per revolution of the pump shaft 5 could be employed.
[0018] The outlet of pump 10 is connected to a plurality of high pressure lines 12 wich
belong to the high pressure section of the injection system.
[0019] The fuel delivered by the pump 10 to this high pressure section of the injection
system and to the high pressure lines 12, can be regulated, depending on the engine
ope rating conditions, within the pump 10 in a manner known from already employed
in-line or distributor type fuel injection pumps.
As shown in the drawings, this regulating process is taken care of by an electronic
control unit 20 and appropriate actuators 21 (not shown in detail) placed within the
housing of the pump 10 and connected to the control unit 20 by means of an electrical
connection 19.
[0020] The control unit 20 operates also the solenoid 74 of each injector 4. The main input
signals to the control unit 20 are the crankshaft angle position sensed by a pick-up
sensor 22 and the position of the throttle pedal 24. Further input signals 26 such
as engine coolant temperature, intake air or boost pressure etc. can be fed to the
control unit 20 as well. The control unit 20 is powered by a battery 28.
[0021] The control unit 20 comprises a one-chip microprocessor and the required input and
output power modules. The desired relationships between the input signals and the
output signals to the injector solenoids 74 and to the actuator 21 of the pump 10
is programmed into the microprocessor. The required data needed to determine the momentary
value of the output signals as a function of the momentary input signals are stored
in the microprocessor memory. The microprocessor can also be used to perform troubleshooting
diagnostics of the combined engine and fuel-injection systems.
[0022] The high pressure section of the injection system of Fig. 1 consists of the high
pressure pipes 12 and of the high pressure section 34 of each injector 4. From each
injector 4 a low pressure spill pipe 38 and a low pressure pipe 40 connecting all
pipes 38 returns low pressure fuel released form each injector 4 back to the fuel
tank 6.
[0023] The design of the high pressure section 34 of each injector 4 will be discussed later
in connection with Fig. 2.
[0024] It is important to note at this point that each high pressure pipe 12 provides for
a direct flow path without any restriction from the high pressure pump 10 to each
injector 4. As shown in the detail A of one of the injectors 4, a direct and unrestricted
hydraulic connection is made between the outlet side of the high pressure pump 10
to the region around the seat of the injector needle valve in the tip of each injector
4 by means of the high pressure pipes 12 and the high pressure section 34 of the injector
4.
[0025] With the above mentioned layout of the high pressure section of the injection system
of Fig. 1 consisting of high pressure pipes 12 and of one high pressure section 34
in each injectior 4 it is possible to eliminate any fuel plenum chambers as well as
an accumulator volume placed within the injector's body as described in German published
patent application 37 27 742 (corresponding to U.S. patent specification 4,566,416)
and German published patent application 31 26 393.
[0026] The essential features of the fuel injection system of the present invention are
as follows:
- the entire fuel volume enclosed under high pressure in the lines 12 and sections
34 of each injector 4 hydraulically communicates within this high pressure section
in an unhindered, unrestricted way,
- the cross sectional areas of all high pressure passages leading form the outlet
of the pump 10 to the region around the seat of the injectors 4 of the injection system
is substantially bigger preferably at least 10 times bigger, than the combined cross
sectional area of all injection orifices of one injector 4,
- during engine operation the entire high pressure section is permanently pressurized
to a pressure substantially equal to the injection pressure suitable at given engine
running conditions.
[0027] According to the present invention it is therefore possible to largely reduce the
total high pressure volume of the injection system (by over an order of magnitude)
compared to the prior art systems referred to earlier. This allows to achieve a fast
response during transient operation of the engine 2, which allows to employ the injection
system also for example for passenger car engines without the need of an ov
erdimensioned pump 10 or of a complex control sheme taking care of the transient engine
operating conditions.
[0028] The reduction of the pressurized fuel volume to a minimum suited for a given application
is a big advantage of the fuel injection system according to the present invention.
[0029] However, due to pressure waves arising in a system as just described, an injector
design insensitive to pressure waves must be used in conjunction with this system
in order to maintain the desired uniformity of fuel delivery of the injectors 4. A
preferred design of such an injector 4 is shown in Fig. 2.
[0030] If the injection system of the present invention is used in an engine with a wide
speed range, such as a passenger car engine, it is important that each pumping event
takes place over a large angle of rotation of the engine crankshaft 7. In the discussed
arrangement of Fig. 1 with a two plunger pump, driven by the engine with a drive ratio
of 1:1, each pumping event takes place over 180 degrees of rotation of the crankshaft
7.
[0031] The slow, harmonic pumping motion makes it possible to avoid high pressure peaks
at a high engine speed, which would be detrimental to the mechanical durability of
the components of the injection system. At the same time, due to the fact that there
is no relationship between the momentary pumping rate of the pumping plungers and
the injection rate of any of the injectors 4, the injection pressure can be maintained
at a high level when the engine speed is slow. Both attributes allow to optimise the
engine performance with respect to power, noise and emissions.
[0032] It is furthermore important that, as shown in Fig. 1, the injection system's high
pressure section is built in such a way that it is symmetrical with respect to the
arrangement of the fuel lines 12. Accordingly, the time of a pressure wave to travel
from anyone of the injectors 4 to the outlet side of the pump 10 or vice-versa will
be the same for all injectors 4 employed.
[0033] In an alternate arrangement of the injection system according to the present invention
(not shown in Fig. 1) each injector 4 is connected by fuel lines 12 of equal length
directly to the housing of the pump 10. In this case a hydraulic connection between
the fuel lines 12 would also be provided within the housing of the pump 10.
[0034] Fig. 2 shows the main portion of an injector 4 of preferred design, which can be
employed advantageously in conjunction with the injection system of Fig. 1. The pressurized
fuel coming from one of the high pressure lines 12 shown in Fig. 1 enters the injector
4 through bore 42, which is machined into the housing 44 of the injector 4. The bore
42 is connected to a bore 54 which extends downwards in axial direction to the needle
valve seat 56.
[0035] An injector needle valve 52 is arranged within the bore 54 and extends downwards
into the injector neck 55 and to the needle valve seat 56. As shown in Fig. 2 the
tip of the needle valve 52 is engaged with the valve seat 56 and closes the injection
orifices 58 thus preventing pressurized fuel to be injected from the bore 54 through
the seat 56 and the injection orifices 58 into the combustion chamber of the related
internal combustion engine (not shown). As already mentioned, the cross sections of
the flow passages from bore 42 to the valve seat 56 are big compared to the total
cross sectional flow area of all injection orifices 58. The needle valve 52 can be
momen tarily axially shifted in order to open the injection orifices 58 and to allow
injection of a desired quantity of fuel.
[0036] On the end opposite to its tip, the injector needle valve 52 is provided with a needle
valve piston 60 with two sections of different outer diameters. The outer diameter
of the lower section 63 is tightly matched to the inner diameter of a guide-piece
62. The latter has an enlarged portion which, together with a sealing ring 64, is
pressed against a shoulder 44a of the injector housing 44 by a
n internal hexagon-screw 66, thus sealing the high pressure section of the injector
4.
[0037] The outer diameter of the upper section 69 of the needle valve piston 60 is larger
than the outer diameter of the lower section 63. The needle valve piston 60 with its
two sections 63, 69 of different outer diameters is firmly connected to the injector
needle valve 52, either because it is made of one piece with the injector needle valve
52 as shown on Fig. 2, or by firmly connecting the two parts 52, 60 to one another,
for example by press-fitting or by welding the parts together. A bore 65 machined
in the inner part of the needle valve piston 60 is connected at one end to the bore
54 of the injector 4. The other end of bore 65 is connected to a restricted orifice
67 with a substantially smaller flow cross sectional area compared to the cross sectional
area of bore 65. The other end of the orifice 67 extends through the upper end surface
69a of the thicker section 69 of the needle valve piston 60.
[0038] The outer diameter of the thicker section 69 is tightly matched to the inner bore
71a of a cylindrical piece 71 which is closed at one end and provided with an orifice
70 opening into a chamber or space 72. The latter is defined by the piece 71 and by
the thicker section 69 of the needle valve piston 60. Both orifices 67 and 70 are
axially aligned and extend along the longitudinal axis 4a of the injector 4.
[0039] A solenoid valve S is provided having a solenoid 74 which actuates a valve stem 76.
As shown in Fig. 2 the valve stem 76 is closing the outlet of the orifice 70, thus
preventing fuel to flow through the orifice 70 into the neighbouring low pressure
region 78 which is connected the return line 38 (see also in Fig. 1). The piece 71
will be pushed by the fuel pressure in the chamber 72 against a flat surface 79a of
a support 79, which determines the axial position of the piece 71 and guides at the
same time the valve stem 76.
[0040] As an important matter, the piece 71 is guided in a tight fit relationship at an
inner surface 71a only by the thicker section 69 of the needle valve piston 60. The
outer surface 71b of the piece 71 is not guided. This allows a substantially seal-tight,
leak-free design and an unhindered axial motion of the injector needle valve 52 during
the injection event. If the piece 71 had to be guided also at its outer surface 71b,
due to the tight fits needed for reasons of fluid seal tightness, jammming of the
neddle valve piston 60 or at least undesired high frictional forces could occur in
case the tight fits needed for a tight seal are not perfectly concentrical to one
another.
[0041] The mode of operation of the injector 4 is as follows:
[0042] When at a desired point in time the solenoid 74 is energized by an electric pulse
of a predetermined duration coming from the control unit 20, the valve stem 76 is
retracted from its seat and the outlet of the orifice 70 is opened. The pressure in
the chamber 72 will abruptly drop, due to the formation of a single fuel jet in the
two aligned orifices 67 and 70. The fuel pressure acting on the underside 63a of the
lower section 63 of the injector needle valve piston 60 can now shift the needle valve
52 in its opened position and the injection event begins by discharging fuel through
the injection orifices 58. The release of fuel results in a negative pressure wave
which propagates from the injector 4 into the high pressure section of the injection
system of Fig. 1.
[0043] If the electric pulse to the solenoid 74 is interrupted, the solenoid valve 76 is
shifted back to its seat at the outlet of the orifice 70 by the spring 78. The pressure
in the space 72 will abruptly rise. Since the upper surface 69a of the upper, thicker
section 69 is greater than the lower surface 63a of the lower, thinner section 63
of the needle valve piston 60, a force to quickly reseat the injector needle valve
52 and thus terminate the injection event results, even if the fuel pressure in the
bore 54 is equ al to the pressure in the space 72. Even a pressure
wave in the system does not noticeably disturb the closing of the injector needle
valve. This is not the case in the solution disclosed in the German published patent
application 32 27 274 where the injector needle valve piston is of a uniform outer
diameter. In this case a pressure wave acting on the underside of the needle valve
piston would drastically effect the closing behaviour of the injector needle valve
and thus the uniformity of fuel delivery. For this reason an accumulator chamber within
the injector housing and an orifice between this accumulator and the fuel supply line
had to be provided in this prior art system to ensure a repeatable closing behaviour
of the injector needle valve.
[0044] The mentioned pressure waves have an influence on the shape of the injection rate
during the injection event. To make sure that all injectors of a multicylinder engine
do have the same performance it will be suitable to build the high pressure section
of the injection system of Fig. 1 symmetrically.
[0045] In an alternative layout of the fuel injection system according to the present invention
shown in Fig. 3, the electronic control unit 20 controls an electrically driven high-to-low
pressure spill valve 80. The electrical connection 19 and the actuator 21 within the
housing of the pump 10 in the embodiment of Fig. 1 can be eliminated. In this case
the high pressure pump 10 will have a constant fuel delivery per revolution of the
pump shaft 5, which will be entirely pumped into the high pressure lines 12 (except
for some leakage of the pump 10).
[0046] The spill valve 80 is of the on/off type valve, timed by the control unit 20 in a
suitable way to release the ex cess fuel delivered by the pump 10 in a return line
30 and establish the desired pressure in the lines 12 according to the operating conditions
of the engine 2. An electrical connection 82 connects the control unit 20 with the
electrically driven on/off spill valve 80. The valve 80 could also be a very sensitive
adjustable pressure regulator valve capable to even out to some extent undesired pressure
pulsations generated by the fuel pump 10 or induced by the injectors 4.
[0047] The power demand of the pump 10 for part-load running conditions of engine 2 will
in this case be somewhat higher compared to the design of Fig. 1, since fuel in excess
must be pressurized. However, the layout of Fig. 3 allows to achieve another advantage
as explained below.
[0048] If the spill valve 80 is an electrically driven on/off valve, when it is switched
on by means of an electric signal of the control unit 20, fuel will flow in the line
section 12a from the pump 10 to the valve 80. When the valve 80 is switched off the
moving fuel column in line 12a will be stopped and a positive dynamic pressure wave
will propagate upstream of the valve 80 into the line 12a as well as into the remaining
lines 12 leading to the injectors. After a given travel time this positive dynamic
pressure wave will reach the seat 56 (see also Fig. 2) of one or more injectors 4.
[0049] By timing the off-signal of the valve 80 appropriately by means of the control unit
20 in such a way that the positive dynamic pressure wave arrives at an injector 4
when the injection event begins, it is possible to obtain a higher effective injection
pressure (in the amount of 20 to 30%) compared to the static pressure without the
positive dynamic pressure wave. This allows to rise the effective injection pressure
at full load engine running conditions, when a high injection pressure is required.
Also, since in this case the pump 10 must generate a lower pressure, less mechanical
input power on shaft 5 is required.
[0050] Since the timing of the off-signal of the valve 80 is determined by the electronic
control unit 20, it can be governed flexibly to obtain the desired effect for all
injectors 4 employed in the injection system as well as, if needed, at different engine
running speeds an d load conditions. It has to be noted that
the essential criteria of the injection system of the present invention, as explained
earlier while describing Fig. 1, must still apply in order to benefit of the advantage
of said positive dynamic pressure wave.
[0051] In a second alternative layout of the fuel injection system according to the present
invention, shown in Fig. 4, the pump 10 pumps the fuel into high pressure pipes 14,
which are connected to two check valves 16 and 17 and to a discharge valve 18. The
check valves 16 and 17 could for example be spring loaded ball valves. The pump 10
and the discharge valve 18 work together in an analogous manner as pump 10 and spill
valve 80 of the embodiment shown in Fig. 3. Discharge valve 18 is connected to a return
line 30 and is controlled by control unit 20 via an electrical connection 33. The
fuel pressure in the lines 14 will be maintained by the discharge valve 18 at a pres
sure level according to and appropriate for given operating conditions of the engine
2.
[0052] It is important to note that the high pressure fuel line sections 14 are permanently
under a high fuel pressure during operation of the engine 2 and are arranged between
the outlet side of the pump 10 and the check valves 16 and 17. The pump 10, as in
many other known hydraulic systems, must also have at least one additional check valve
placed within the pump housing upstream to the high pressure outlet of the pump 10.
This additional check valve is not shown in Fig. 1, 3 and 4.
[0053] It must be noted that, by a suitable layout of each one of the check valves 16 and
17, the fuel flow in the direction from the line sections 14 across a check valve
16 or 17 into the subsequent part, i.e. lines 12, of the injection system can occur
practically undisturbed. The flow path in this direction is thus substantially unrestricted.
Only in the opposite direction the flow is blocked. As a consequence, the fuel injectors
4 are always under a high fuel pressure during engine operation, not only during the
intermittent injection event of any of the injectors, as it is the case in the system
disclosed in U.K. published patent application.
[0054] Downstream of the check valves 16 and 17 are formed two hydraulically separate groups
of high pressure lines 12 and injectors 4, each one of them being connected to one
check valve. This arrangement can be advantageously employed in engines having many
cylinders, such as 6, 8 and 12 cylinder engines. Groups of 2 or more injectors, each
one communicating with one check valve, can be formed in a suitable way according
to the firing order of the engine cylinders. The pressure waves induced during each
injection event by each injector in the lines 12 within one group cannot propagate
into another group, and critical overlapping of such pressure waves that can create
unstable injection conditions will be avoided. On the other hand, only the group with
a lower fuel pressure will be filled through one check valve by the fuel coming from
the pump 10.
[0055] The control scheme shown in Fig. 1 could also be used to match the high pressure
fuel delivery to the high pressure fuel demand of the injection system.
[0056] As an important matter, the injectors 4 within one such group shall be hydraulically
communicating with one another in an unrestricted way, substantially as described
earlier in connection with the embodiment of Fig. 1.
[0057] As shown in Fig. 4 by dotted lines, one additional fuel chamber 36 per injector group
may be added as an alternative for some specific applications where it is more practical
to add a fuel chamber in order to optimize the total volume of pressurized fuel within
one group.
[0058] While preferred embodiments of the present invention have been described for purposes
of illustration, the foregoing description should not be deemed a limitation of the
invention herein. Accordingly, various modifications, adaptations and alternatives
may occur to one skilled in the art without depart ing from the
spirit and scope of the present invention.
1. Fuel injection system for an internal combustion engine (2) comprising at least
one electromagnetically operated fuel injector (4) for injecting pressurized fuel
into a combustion chamber of the internal combustion engine (2), said at least one
fuel injector (4) having a body portion (44) with a valve seat (36), at least one
discharge orifice (58) and an injector valve member (52) cooperating with said valve
seat (56) for closing said discharge orifice (58) and being shiftable to be momentarily
lifted from said valve seat (56) for opening said discharge orifice (58) and discharging
pressurized fuel into a combustion chamber of the internal combustion engine, said
fuel injection system further comprising a high pressure fuel pump (10) driven by
the internal combustion engine (2), at least one injection line (12, 14, 42) leading
from said pump (10) to said at least one fuel injector (4) and providing a fuel flow
path from said pump (10) to a region (54) immediately upstream of said valve seat
(56), the cross sectional area of said fuel flow path (12, 14, 42) leading from said
pump (10) to said region (54) upstream of said valve seat (56) being substantially
bigger than the total cross sectional area of all injection orifices (58) of said
at least one fuel injector (4), said fuel flow path (12, 14, 42) being substantially
free of flow restrictions to allow a substantially unrestricted fuel communication
between said pump (10) and said region (54) around and immediately upstream of said
valve seat (56), the fuel pressure in said fuel flow path (12, 14, 42) before, during
and after an injection event being substantially equal to the fuel injection pressure.
2. Fuel injection system according to claim 1; wherein the frequency of the pumping
strokes of said fuel pressure pump (10) is the same or an entire mutiple of the frequency
of the injection events of the totality of the injectors (4).
3. Fuel injection system according to claim 1, wherein said fuel pump (10) is provided
with a drive shaft (5) driven by the crankshaft (7) of the internal combustion engine
(2), the drive ratio between said crankshaft (7) and said drive shaft (5) being 1:1
or an entire multiple of 1:1.
4. Fuel injection system according to claim 1, wherein said fuel pump (10) comprises
pumping plungers, said pumping plungers are movable according to a harmonic function.
5. Fuel injection system according to claim 4, wherein anyone of the injection events
takes places during part of a pumping stroke of anyone of said pumping plungers.
6. Fuel injection system according to claim 1, further comprising an electrically
operated spill valve (80; 18) connected to said high pressure injection line (12,
14, 42) and a low pressure return line (30), and a control unit (20) for controlling
the opening and closing of said spill valve (80; 18) for spilling fuel delivered by
said fuel pump (10) into said return line (30) in order to adjust the quantity of
fuel delivered by said pump (10) to said at least one injector (4).
7. Fuel injection system according to claim 6, wherein said fuel pump (10) delivers
a constant amount of fuel per pumping stroke.
8. Fuel injection system according to the claim 6; wherein the timing for the signal
to close the spill valve (80; 18) is choosen by the control unit (20) in such a way
that the pressure wave induced in said injection line (12, 14, 42) by closing said
spill valve (80; 18) reaches the region (54) immediately around and upstream of said
valve seat (56) of said at least one injector (4) immediately before orduring the
momentary opening of said discharge orifice (58) of said injector (4).
9. Fuel injection system according to claim 1, comprising at least four fuel injectors
(4) arranged in groups of at least two fuel injectors (4), the injectors (4) of each
group being connecte d to one another by means of
fuel connection lines (12) providing an unrestricted fuel flow path, the injectors
(4) of each group being further connected to a common fuel supply line(12, 12a, 14)connected
to the outlet of said fuel pump (10).
10. Fuel injection system according to claim 9, comprising a check valve (16, 17)
arranged between said common fuel supply line (14) and each fuel connection line (12)
connecting the injectors (4) of each group, said check valve (16, 17) preventing the
flow of fuel in the direction towards said common fuel supply line (14).
11. Fuel injection system according to claim 10, further comprising a fuel chamber
(36) for each group of injectors (4), said fuel chamber (36) being arranged symmetrically
with regard to the injectors (4) of the associated group and being connected to all
injectors (4) of the respective group by means of fuel lines (12) providing an unrestricted
fuel flow path.
12. Fuel injection system according to claim 1, wherein the length of the fuel flow
path from said fuel pump (10) to said region (54) immediately upstream of said valve
seat (56) is the same for all of said fuel injectors (4).